Hyperhomocysteinemia (Hhe) is an independent risk factor for both systolic and diastolic heart failure. Data from our laboratory demonstrate that Hhe leads to myocardial fibrosis and diastolic dysfunction. Diastolic dysfunction and Hhe are more prevalent in the rapidly increasing older population. Hence, it is crucial to understand the mechanisms involved in Hhe's effects on the myocardium, so that it will be possible to devise appropriate preventive and treatment strategies to combat the epidemic of heart failure. Our preliminary data strongly suggest that Hhe acts via increased oxidant stress in cardiac fibroblasts to cause myocardial fibrosis and diastolic dysfunction. Dietary selenium is a potential major modulator of Hhe-induced myocardial fibrosis, since a major cellular defense against oxidant stress is the selenium requiring enzyme glutathione peroxidase- 1 (GPx-1). Based on our preliminary observations, homocysteine decreases GPx-1 activity and increases oxidant stress and collagen secretion in cultured cardiac fibroblasts, and selenium prevents these effects. The proposed project will test the central hypothesis that selenium modulates Hhe-induced myocardial oxidant stress and fibrosis by altering GPx-1 activity. We will address this central hypothesis through three Specific Aims. First, we will determine the extent to which Hhe-induced myocardial fibrosis is modulated by GPx-1, utilizing male and female mouse models that demonstrate markedly reduced, normal and increased expression of GPx-1 and treated with our well characterized dietary model of Hhe. Plasma and myocardial markers of oxidant stress, expression and activity of GPx-1 and other enzymes involved in the regulation of oxidant levels, myocardial collagen expression, as well as changes in cardiomyocytes, mast cells, vascular smooth muscle cells and endothelium will be measured. Based on our preliminary data, we will also examine for activation of the p38 mitogen activated protein kinase (MAPK) system as the main signal transduction pathway linking Hhe-induced oxidant stress to myocardial fibrosis. Second, we will determine the extent to which selenium modulates Hhe-induced myocardial fibrosis via altered GPx-1 activity. The same mouse models utilized in the first aim will be treated with diets that will create Hhe combined with deficient or excess dietary selenium. Third, we will determine if selenium modulates homocysteine's profibrotic effects by altering GPx-1 activity in cardiac fibroblasts. We will isolate cardiac fibroblasts from the mouse models with varying GPx-1 expression described above and will then study oxidant stress, expression and activity of GPx-1 and other pro- and anti-oxidant enzymes, activation of p38MAPK, and collagen metabolism, after exposure to varying levels of homocysteine and selenium. The applicant's expertise with Hhe-induced myocardial fibrosis and dysfunction, coupled with strong support from the laboratories of Dr. Joseph Loscalzo, a world renowned expert on Hhe, oxidant stress and cardiovascular disease, and Dr. Diane Handy, an expert on the biochemistry of selenium and GPx-1, positions us uniquely to conduct the proposed research. RELEVENCE: A high blood homocysteine level is widely prevalent in the general population and is a potential major contributor to the heart failure epidemic in the United States. Our proposal examines the hypothesis that dietary selenium intake, by enhancing anti- oxidant protective mechanisms in the heart, could be a powerful modulator of heart failure induced by high homocysteine levels. The results of these investigations could lead to novel preventive and treatment strategies to reduce the burden of heart failure in the Unites States.